I'm also a big fan of the 39xx-series. I own or have owned 4 different 3953's (2 standard models; a PC "CCO" (my term, not theirs) and a TSW; also a standard 3913 and 3913LS models and even a CS9. (I no longer own all of them.) The single-stack 9mm 3rd generation S+W autos are excellent, excellent guns for carry and the range. I've focused on them because I wanted to carry what I shoot with the most and I've often said they were the perfect balance: small, light and thin enough for use as a great carry gun while still being "big and heavy enough" for tons of fun on the range.
My Shield is only my second "modern polymer" pistol after my M+P9c. I think time will obviously tell on the Shield long-term, although most reports are extremely positive. My own experience with it is also extremely positive. Some would say the Shield is the modern day alternative to the 3913. I'm leaning that way. I'll be hanging on to most or all of my 3rd gens, but the Shield is getting a lot of range time and just about all my carry time.